Packaging of High Power Semiconductor Lasers

In this chapter, we will give a general description on the basics of semiconductor lasers. Starting with a general introduction about semiconductor lasers, other important specific basics for high power semiconductor lasers are also introduced, covering the fundamental principles, device structures, and basic characteristic parameters.

Semiconductor lasers can be divided into many types according to different classification criteria, such as cooling types, die bonding techniques, and the arrangement of the chips or bars in the assembly. In this chapter, the packaging structures of semiconductor lasers are divided into two categories which are open packages and fiber-coupled modules. The basic and typical structures of the two categories are discussed in detail according single emitters, single bars, and laser stacks.

Thermal management of high power lasers is critical since the junction temperature rise originating from large heat fluxes strongly affects the device characteristics, such as wavelength, power, threshold current, efficiency, and reliability. In this chapter, the temperature effect on the performances of high power semiconductor lasers is introduced in Sect. 3.1; the heat generation sources in semiconductor lasers are analyzed in Sect. 3.2; thermal modeling, design, and analysis are discussed in Sect. 3.3. Furthermore, some thermal management techniques for reducing the junction temperature of the diode laser devices are proposed, including optimization of the cooling structure, cooler design, and packaging materials.

Thermal stress occurring during the packaging and operating processes influences the performance and reliability of high power semiconductor lasers. The stress is mainly caused by the coefficients of the thermal expansion (CTE) mismatch between the mounting substrate and laser chip. Ideally, packaging materials with high thermal conductivities and CTEs matching those of the semiconductor materials such as GaAs, InP, and GaN are desired in high power diode laser packaging. Thermal stress is one of the most critical problems in packaging of high-power diode lasers. In this chapter, effects of the thermal stress on the optical, electrical, and mechanical performances of the semiconductor lasers are investigated, such as wavelength, polarization, smile, and cracking. Formation of thermal stress in high power semiconductor laser is discussed, and approaches to reduce the thermal stress are proposed.

With improving of the performances, semiconductor lasers are becoming attractive as light sources in many fields, such as direct material processing, high power solid-state laser and fiber laser pumping, medical and display applications. However, the poor beam quality is still the main bottleneck limiting their further applications. In order to expand the applications of semiconductor lasers, beam shaping and optical design are essential. Generally speaking, the poor beam quality is due to the waveguide properties of the active region of semiconductor lasers. In this chapter, we will discuss the beam performances of semiconductor lasers in Sect. 5.1. The beam shaping and fiber coupling principles and design methods of a single emitter, a bar, and a stack will be discussed in Sect. 5.2. Section 5.3 presents beam combining and high brightness techniques.

The performance of semiconductor lasers is greatly affected by the properties of packaging materials, which mainly consist of diverse bonding solders, mounting substrates [1–4]. The selection of packaging materials is multidisciplinary and involves achieving a balance among device performance, reliability, manufacturability, and cost-effectiveness. In this chapter, the properties of solder materials, as well as mounting substrates employed in the packaging of high power semiconductor lasers are presented and the effects of material properties on the performance of semiconductor lasers are analyzed in details.

Despite the many advances in manufacturing of high power semiconductor lasers, the basic packaging process has not been changed significantly. This chapter reviews the steps used to package and assemble high power semiconductor laser with open packages and fiber-coupled modules. The fabrication procedure of open packages contains a sequence of processes, which involve incoming materials inspection, raw materials cleaning, metallization, solder deposition, die bonding, wire bonding, assembling, screening, before burn-in (BBI) test, burn in (BI), after burn-in (ABI) test, and final inspection. The details are presented in Sects. 7.1–7.10. Fiber-coupled modules typically use an open package, optics, and a fiber to couple the light into the fiber. The packaging process for fiber-coupled module is introduced in Sect. 7.11.

High power semiconductor laser is a compact and precision optoelectronic device manufactured by a series of complicated fabrication processes. The performances of a semiconductor laser, such as its output power, wavelength, and spectrum are important for applications. Testing of the common parameters of a semiconductor laser is a route process for users for incoming material quality control and manufacturing procedure. Furthermore, testing is a part of semiconductor laser manufacturing process as well. Besides testing, characterization of some uncommon but important features is very important in the development of high power semiconductor lasers and failure analysis. By characterization of these features, such as spatial spectrum, smile and transient thermal impedance, one can have a deep understanding of the behavior of the diode laser, investigate the physics behind the features, and find out a solution to improve the performance and property of the devices.

High reliability and durability are two of the important requirements for a commercially used semiconductor laser. There are multiple causes for the semiconductor laser to fail during operation. Therefore, it is important to analyze and identify the root causes for laser failures and provide effective solutions to improve the reliability and durability of the semiconductor laser. In this chapter, different failure modes of semiconductor lasers are introduced. By analyzing these failure modes, some approaches to improve reliability of the semiconductor laser are demonstrated. The lifetime prediction of the semiconductor lasers is also presented.

At early stage, high power semiconductor lasers have been mainly applied in pumping of solid-state lasers and fiber lasers. However, with the development of chip/bar technology and packaging technology in recent years, semiconductor lasers as light sources have been directly used in many new fields, such as medical and cosmetic, IR illumination, and material surface processing which includes cladding, hardening, and annealing [1–3]. The main applications of semiconductor lasers are shown in Fig. 10.1 [4]. In this chapter, we discuss the applications of high power semiconductor lasers in pumping of solid-state and fiber lasers, in material surface processing as well as medical and cosmetic fields. For pumping application, we mainly discuss the advanced pumping structure and the requirement on semiconductor laser pumping source. For material surface processing application, we introduce a high power semiconductor laser head and discuss its key technologies and applications. For medical and cosmetic, we mainly use laser hair removal as an example to discuss the direct semiconductor laser application in this field.

Driven by lower cost, longer lifetime, and new applications, the requirements of high power semiconductor lasers have been changing and the demand for new products has been accelerated in recent years. As a result, the packaging technologies for high power semiconductor lasers have been advanced rapidly and have become more sophisticated. In this chapter, we review and discuss the technology development trend of high power semiconductor lasers, including single emitters, bars, horizontal bar arrays, and vertical bar stacks. The packaging technology is still one of the bottlenecks of the advancement of high power semiconductor lasers. We will discuss the challenges and issues in high power laser packaging and some approaches and strategies in addressing the challenges and issues will be presented. The application and price trend are also discussed briefly in this chapter.